1. Field of the Invention
The present invention relates to a fuel cell power supply device for controlling the amount of reactive gases supplied to a fuel cell depending on the electric energy requested by a load on the fuel cell.
2. Description of the Related Art
There have heretofore been employed fuel cell power supply devices which use fuel cells as a power supply device for vehicles such as electric vehicles. The amount of electric energy generated by a fuel cell varies depending on the amount of reactive gases consumed thereby, i.e., a reducing gas such as hydrogen or the like and an oxidizing gas such as air or the like for extracting electrons by reacting with the reducing gas. Therefore, if the supplied amount of the reactive gases is larger than the consumed amount of the reactive gases which is required to produce an amount of electric energy depending on the amount of electric energy requested by a load such as an electric motor or the like on the fuel cell, then a certain amount of the reactive gases is wasted.
If the actually supplied amount of the reactive gases is smaller than the consumed amount of the reactive gases which is required to produce an amount of electric energy depending on the requested amount of electric energy, then the fuel cell runs short of the reactive gases, and the electrolytic membrane of the fuel cell is deteriorated, resulting in a reduction in the performance of the fuel cell.
One conventional fuel cell power supply device incorporates a control arrangement shown in FIG. 3 of the accompanying drawings for determining a target amount of generated electric energy (Ifc_CMD) for a fuel cell on a vehicle. When electric energy starts being supplied from the fuel cell to an electric motor, a requested-amount-of-electric-energy calculator 100 determines a requested amount of generated electric energy (Ifc_CAL) required by the fuel cell depending on the amount of depression (Ap) of the accelerator pedal, the vehicle speed (Nm) of the vehicle, and the consumed amount of electric energy (Pload) used by electric accessories other than the electric motor.
While electric energy is being supplied to the electric motor, an actual amount of electric energy (Ifc) generated by the fuel cell is detected, and a subtractor 101 calculates the difference between the actual amount of generated electric energy (Ifc) and the requested amount of generated electric energy (Ifc_CAL). The calculated difference is processed according to a PID control process by a PID controller 102, which produces a corrective quantity (Ifc_AMD). An adder 103 adds the corrective quantity (Ifc_AMD) to the requested amount of generated electric energy (Ifc_CAL), thus calculating a target amount of generated electric energy (Ifc_CMD). The supply of reactive gases to the fuel gas is controlled such that the reactive gases are supplied to the fuel cell in an amount depending on the target amount of generated electric energy (Ifc_CMD).
By thus correcting the requested amount of generated electric energy (Ifc_CAL) depending on the difference between the actual amount of generated electric energy (Ifc) and the requested amount of generated electric energy (Ifc_CAL) to calculate the target amount of generated electric energy (Ifc_CMD), the effect of variations of the electric energy consumed by the electric motor and the electric accessories is suppressed to stabilize the target amount of generated electric energy (Ifc_CMD).
The control arrangement shown in FIG. 3 for calculating the target amount of generated electric energy (Ifc_CMD) and controlling the amount of the reactive gases supplied to the fuel cell in an amount depending on the target amount of generated electric energy (Ifc_CMD) suffers the following problems: When the load on the fuel cell increases abruptly, the PID controller 102 and the adder 103 perform a corrective action to prevent the target amount of generated electric energy (Ifc_CMD) from increasing. As a result, the transient response of the fuel cell is lowered, causing the fuel cell to suffer a lack of the reactive gases.